The continual demand for enhanced integrated circuit performance has resulted in, among other things, a dramatic reduction of semiconductor device geometries, and continual efforts to optimize the performance of every substructure within any semiconductor device. A number of improvements and innovations in fabrication processes, material composition, and layout of the active circuit levels of a semiconductor device have resulted in very high-density circuit designs. Increasingly dense circuit design has not only improved a number of performance characteristics, it has also increased the importance of, and attention to, semiconductor material properties and behaviors.
The increased packing density of the integrated circuit generates numerous challenges to the semiconductor manufacturing process. Nearly every device must be smaller without degrading operational performance of the integrated circuitry. High packing density, low heat generation, and low power consumption, with good reliability must be maintained without any functional degradation. Increased packing density of integrated circuits is usually accompanied by smaller feature size and, correspondingly, smaller device geometries.
At the same time, the use of electronic products and systems has spread into a number of new and distinct applications—many of which were not, until recently, associated with electronic technology. Often, such new applications place a number of unique demands on circuitry components and substructures. Consider, for example, the radiation tolerance required of satellite or spacecraft systems, or the heat and shock tolerance required of automotive systems.
Thus, optimized performance over a broader range of operating conditions is required of many electronic components and substructures. This has resulted in a number of improvements and innovations in electronic systems, and has increased the importance of, and attention to, component and substructure properties and behaviors.
Commonly, system designers specify or define a number of required operational parameters (e.g., max/min voltage, signal timing) for certain circuitry segments in a system. Semiconductor devices (i.e., integrated circuits) must comply with such required parameters in order to be used in the system. For example, a system may require that a semiconductor device operate over supply voltage range of 0V to 40V, optimized for performance at 20V. In another example, a system may require that a semiconductor device provide a specified timing parameter (e.g., trise(MIN), tfall(MAX)).
Unfortunately, however, there are a large number of variables in semiconductor device manufacturing that can affect any given performance parameter. Intra-process variations, feature matching issues, and layout considerations are among a number of concerns that impact a device manufacturer's ability to provide a specified performance parameter. In some cases, a semiconductor device's standard operational parameters may be sufficient to provide a required performance level in a given system. In a number of other cases, however, a given system may require a very specific or peculiar performance parameter—such that an integrated circuit must be designed specifically for that application, if possible.
Consider, for example, a common driver circuit, such as an amplifier, utilized in a high-voltage application that has specific performance parameters. Commonly, performance specifications require that driver circuitry consume relatively low power while driving a significant load. In a number of applications, an output node from a driver circuit can be coupled to a load having a wide variety of “normal” operating conditions—such as relatively large voltage swings during standard operations. Components and structures within the driver circuit may therefore be adapted to tune the circuit to a required range of operating conditions. Depending upon the design and fabrication processes used, however, certain adapted circuitry components may be susceptible to performance degradation or break down if non-standard conditions (e.g., overload, short) cause output circuitry to exceed the standard operating range.
For example, sustained power overload on certain output circuitry can cause a significant rise in operating temperature, which can—over time—begin to break down transistor structures. Even over a relatively short amount of time, an excessive output energy drop can degrade the performance of output transistor structures, or render them completely inoperable. In addition, increased energy drop across a driver output can significantly increase overall system power consumption. This can cause a number of system inefficiency or reliability issues, or cause significant process yield problems for the device manufacturer.
As a result, a number of protection schemes have been implemented in an attempt to prevent overloading of such output circuitry. Generally, protection schemes rely on some form of all-or-nothing overcurrent protection—implemented as circuitry that shuts down the driver output component(s) every time output current level(s) exceed some arbitrary threshold. Often, this threshold is set at some value within, by at least a nominal margin, the specified operating range of the driver circuitry. Using such schemes, even instantaneous variations in current that exceed the threshold cause output shutdown—even though such variations may still be marginally within the operational capability of the output components, or may last for such a brief period that no damage would actually accrue to the output components if left unchecked. In certain system applications, and especially in signal-intensive applications, minor overcurrent variations (i.e., those that would not otherwise cause damage to an output structure) occur randomly and frequently. Utilizing conventional output protection schemes in such applications could result in a potentially high degree of system inefficiency or cause system malfunction if the signal integrity is sufficiently degraded, as driver output components are repeatedly cycling off and on every time an arbitrary threshold is exceeded.
Other conventional protection schemes err on the side of less comprehensive protection—choosing instead to set protective thresholds well outside of the specified operating range of driver circuitry. Such approaches typically provide a protective cutoff or shutoff only in the case of some catastrophic overload condition. These under-corrective schemes typically do not trigger for overloads that are only marginally outside of the specified operating range of driver circuitry, even if such overloads occur for an extended length of time. These schemes, therefore, are quite capable of permitting extensive damage to output structures, over time.
As a result, there is a need for a system for protective driver output circuitry or structures that effectively limit output energy levels without over or under correcting, thereby reducing device and system inefficiencies or malfunctions introduced by excessive or restrained off-cycling of device output structures—one that is readily adaptable to address a variety of specific parametric requirements, while providing efficient and reliable device performance in an easy, efficient and cost-effective manner.